JP5325610B2 - Metal surface treatment composition, metal surface treatment method using the same, and metal surface treatment film using the same - Google Patents

Description

  The present invention relates to a metal surface treatment composition capable of forming a film capable of imparting excellent corrosion resistance to a metal material, particularly a metal structure having a complicated shape, by a single dipping process, and a metal surface using the same. The present invention relates to a treatment method and a metal surface treatment film using them.

  Conventionally, electrodeposition coating having high throwing power has been generally used as a method for imparting excellent corrosion resistance to various metal materials, particularly metal structures having complicated shapes. However, in many cases, the desired corrosion resistance cannot be obtained only with the electrodeposition coating film obtained by electrodeposition coating. Processing was applied.

  Electrodeposition coating consists of an anionic electrodeposition coating in which a coating is deposited by anodic electrolysis in an aqueous paint containing an anionic resin emulsion, and an aqueous coating containing a cationic resin emulsion. Cathodic electrolysis can be broadly divided into cationic electrodeposition coating in which a coating film is deposited. To improve the corrosion resistance of ferrous metal materials, cationic electrolysis, which does not cause the base metal to elute into the paint during electrolytic treatment, is possible. Electrodeposition coating is advantageous, and cationic electrodeposition coating is widely applied to automobile bodies, automobile parts, home appliances, building materials, etc., which are metal components mainly composed of iron-based materials.

Cationic electrodeposition coating has a long history in the market, and once it was rust-proof by blending chromium and lead compounds. However, since this also had insufficient rust prevention properties, a ground treatment such as a zinc phosphate chemical conversion treatment was essential.
Currently, chromium and lead compounds have become virtually unusable due to environmental regulations, especially the European ELV regulations, so alternative components have been studied and their effects have been found in bismuth compounds. Is disclosed.

  Patent Document 1 (Japanese Patent Laid-Open No. 5-32919) discloses a resin composition for an electrodeposition coating, which contains at least one pigment coated with a bismuth compound.

  Patent Document 2 (WO 99/31187) discloses a cationic electrodeposition coating composition comprising an aqueous dispersion paste containing an aqueous dispersion in which an organic acid-modified bismuth compound is present in a water-insoluble form. ing.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2004-137367) discloses a cationic electrodeposition coating material comprising a colloidal bismuth metal and a resin composition having a sulfonium group and a propargyl group.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-197688) discloses an electrodeposition coating comprising particles of at least one metal compound selected from bismuth hydroxide, a zirconium compound, and a tungsten compound, wherein the metal compound contains 1 to An electrodeposition paint characterized by being 1000 nm is disclosed.

  Patent Document 5 (Japanese Patent Application Laid-Open No. 11-80621) discloses a cationic electrodeposition coating composition containing an aqueous solution of an aliphatic alkoxycarboxylic acid bismuth salt.

  Patent Document 6 (Japanese Patent Laid-Open No. 11-80622) includes an aqueous solution of a bismuth salt with two or more organic acids, wherein at least one of the organic acids is an aliphatic hydroxycarboxylic acid. A cationic electrodeposition coating composition characterized by the above is disclosed.

  Patent Document 7 (Japanese Patent Laid-Open No. 11-100533) discloses a cationic electrodeposition coating composition characterized by containing bismuth lactate using lactic acid containing 80% or more of L isomers among optical isomers. Has been.

  Patent Document 8 (Japanese Patent Laid-Open No. 11-106687) includes an aqueous solution of a bismuth salt containing two or more organic acids, wherein at least one of the organic acids is an aliphatic alkoxycarboxylic acid. A cationic electrodeposition coating composition characterized by the above is disclosed.

  These patent documents can be roughly classified into patent documents 1 to 4 and patent documents 5 to 8. That is, Patent Documents 1 to 4 are those in which a bismuth compound or metal bismuth that is insoluble in an aqueous paint is dispersed, and Patent Documents 5 to 8 dissolve at least the bismuth compound until there is no remaining solids, that is, Bi. It is characterized by being added to the paint after being in an ionic state.

  However, the bismuth compounds in these patent documents only act as substitutes for chromium compounds and lead compounds, and sufficient corrosion resistance cannot be obtained without ground treatment such as zinc phosphate chemical conversion treatment. In fact, these patent documents disclose only examples based on the combination with zinc phosphate chemical conversion treatment.

  On the other hand, recently, a technique has been studied in which corrosion resistance is further improved by a method other than a bismuth compound, and sufficient corrosion resistance can be ensured with one coat without applying a ground treatment such as a zinc phosphate chemical conversion treatment.

For example, Patent Document 9 (Japanese Patent Application Laid-Open No. 2008-274392) discloses a method of forming a film by coating a metal substrate with a film forming agent by at least two stages of multi-stage energization methods, and (i) a film forming agent. Is at least one selected from a zirconium compound and, optionally, titanium, cobalt, vanadium, tungsten, molybdenum, copper, zinc, indium, aluminum, bismuth, yttrium, lanthanoid metal, alkali metal and alkaline earth metal The compound containing metal (a) comprises 30 to 20,000 ppm in terms of total metal (in terms of mass) and 1 to 40% by mass of the resin component, and (ii) the first stage using the metal substrate as the cathode performed by energizing the painting the 1~50V voltage _{(V 1)} 10 to 360 sec 2, then, the metallic substrate as a cathode Wherein the difference in voltage 50~400V eyes after painting done by energizing 60 to 600 seconds _{(V 2),} and (iii) a voltage _{(V 2)} and the voltage _{(V 1)} is at least 10V A method for forming a surface-treated film is disclosed.

  Patent Document 10 (Japanese Patent Application Laid-Open No. 2008-538383) discloses an aqueous coating composition containing (A) a rare earth metal compound, (B) a base resin having a cationic group, and (C) a curing agent, The amount of the rare earth metal compound (A) contained in the coating composition is immersed in an aqueous coating composition in which the amount of the rare earth metal compound is 0.05 to 10% by weight in terms of the rare earth metal with respect to the solid content of the coating. A dipping step, applying a voltage of less than 50 V as a cathode in the aqueous coating composition, and a pretreatment step, and applying a voltage of 50 to 450 V as the cathode in the aqueous coating composition. A method for forming a multilayer coating film including an electrodeposition coating step of applying a voltage is disclosed.

Japanese Patent Laid-Open No. 5-32919 WO99 / 31187 JP 2004-137367 A JP 2007-197688 A Japanese Patent Laid-Open No. 11-80621 Japanese Patent Laid-Open No. 11-80622 Japanese Patent Laid-Open No. 11-100533 JP-A-11-106687 JP 2008-274392 A JP 2008-538383 A

  As a result of various studies on these prior arts, the present inventors have applied Bi in order to form a coating on a metal material that also provides sufficient corrosion resistance without pretreatment such as a zinc phosphate-based chemical conversion coating. The conclusion is reached that is most effective. And we decided to reconsider the effect of Bi.

  And, as a function and effect of Bi, the function of a resin as a curing catalyst and the anticorrosive action of a base metal have been attracting attention in the past, but the function as a curing catalyst can be expected in the prior art, but the anticorrosive action of a metal. Was considered to be a solution to the problem by maximizing this effect.

  The anticorrosive action of the base metal must be on the surface where Bi contacts with the metal, that is, the interface between the base metal surface and the coating, but in the prior art, the Bi component is uniformly dispersed in the coating and exhibits corrosion resistance. It was estimated that sufficient Bi was not present on the base metal surface.

  As described above, Patent Documents 1 to 4 are those in which a bismuth compound or metal bismuth that is insoluble in an aqueous paint is dispersed. When a film is deposited from such a composition, the film is the same as other pigments. Bi is uniformly dispersed therein.

  Patent Documents 5 to 8 are characterized in that at least the bismuth compound is dissolved until there is no remaining solids, that is, Bi ions are added to the coating material, but the organic acid chelate is a Bi stabilizer. Since the ability is weak, Bi is gradually hydrolyzed when it is put into the composition, and changes to oxide or hydroxide, so long-term stabilization as Bi ion cannot be expected. . As a result, Bi is uniformly dispersed in the film. In these patent documents, the fact that the zinc phosphate-based chemical conversion treatment was used as the base treatment also supports the above-mentioned assumption.

  On the other hand, Patent Document 9 and Patent Document 10 are techniques for depositing an inorganic film on a base metal and laminating a resin film, which is advantageous in terms of anticorrosion of the base metal. Both the resin film and the resin film have a mechanism that precipitates due to the pH increase on the surface of the base metal by cathodic electrolysis, so that it is not easy to form a laminated film.

  In order to solve the above-described problems of the prior art, the present inventors applied an aminopolycarboxylic acid having a high chelating ability in order to make Bi ions exist more stably in the composition, and thus applied to low voltage cathode electrolysis. Thus, a reaction mechanism was found in which resin was deposited by such pH increase at the stage where Bi was diffused and reduced by high voltage cathode electrolysis.

And the film obtained by this confirms that the corrosion resistance of the base metal can be sufficiently improved by Bi present in a high concentration on the surface of the base metal as well as the curing catalyst ability of the resin of Bi. The invention has been completed.
That is, the present invention includes the following (1) to (4).

(1) 5 to 30% by weight of nonionic and / or cationic resin emulsion containing 100 to 1000 ppm of trivalent Bi ion and 0.5 to 10 times molar concentration of aminopolycarboxylic acid with respect to Bi ion A composition for electrodeposition coating (a metal surface treatment composition for depositing an organic-inorganic composite film by electrolysis).
(2) The electrodeposition coating composition according to (1) above, which contains 20 to 500 ppm of trivalent Al ions.
(3) After immersing the metal material having a cleaned surface in the composition of (1) or (2), the electrolysis step (1) using the metal material as a cathode, that is, a voltage of 0 to 15V. Electrolysis for 10 to 120 seconds and electrolysis step (2), ie, for 30 to 300 seconds at a voltage of 50 to 300 V, and the electrolysis step (1) is electrolyzed prior to the electrolysis step (2). And then performing washing with water and baking to deposit a film on the metal material. Here, the “voltages X to Y (V)” in the electrolysis steps (1) and (2) may be a mode in which a constant voltage is applied within the range of the voltages X to Y or a mode in which the applied voltage is changed over time. Good. In addition, the lower limit “0V” of “voltage 0 to 15V” in the electrolysis step (1) means a voltage at a predetermined time in an aspect in which the applied voltage is changed over time, not in a constant voltage aspect.
(4) Using the composition of (1) or (2) above, metal Bi and oxidized Bi are deposited as Bi in an amount of 20 to 250 mg / m 2 by the treatment method of the invention (3), and the total film thickness is 5 to It is 40 μm, and the Bi adhesion amount on the metal material side from the center of the film thickness: B is a Bi adhesion distribution that is 55% or more (B / A ≧ 55%) with respect to the total Bi adhesion amount A. Characteristic metal surface treatment film.

FIG. 1 is an electrolysis pattern in Examples and Comparative Examples. FIG. 2 is an EPMA line analysis profile of the film in Example 3. FIG. 3 is a diagram showing appropriate ranges of Al ion concentration and pH.

  The metal surface treatment composition, metal surface treatment method and metal surface treatment film of the present invention are used for the purpose of preventing various metals from corrosion. The metal material is not particularly limited, but steel materials such as cold-rolled steel plates, hot-rolled steel plates, casting materials, steel pipes, etc., and zinc-based plating treatment and / or aluminum-based plating are applied on those steel materials. Materials, aluminum alloy plates, aluminum castings, magnesium alloy plates, magnesium castings, and the like. It is particularly suitable for use in metal structures having complicated shapes, for example, automobile bodies, automobile parts, home appliances, building materials, etc., which are metal structures mainly composed of iron-based materials.

  The metal surface treatment composition of the present invention preferably contains 5 to 30% by weight of a nonionic and / or cationic aqueous resin based on the total weight of the composition. It is more preferably 7 to 25% by weight, and most preferably 10 to 20% by weight. If the resin content is too low, the amount of film deposition is insufficient, and if the content is too high, it is economically disadvantageous. Here, neither a nonionic resin nor a cationic resin is particularly limited. Hereafter, the manufacture example of each resin is shown.

  For the nonionic resin emulsion, either or both of a method of introducing a nonionic functional group such as ethylene oxide into the base resin, that is, a self-emulsification method and a method of emulsification using a nonionic surfactant, that is, a forced emulsification method. It can be produced using a technique. For the cationic resin emulsion, either or both of a method of introducing a cationic functional group such as an amine group into the base resin, that is, a self-emulsification method and a method of emulsification using a cationic surfactant, that is, a forced emulsification method, are used. They can be used at the same time. Furthermore, after introducing a cationic functional group, a nonionic surfactant can also be used as an emulsification aid. Moreover, when the molecular weight of the self-emulsifying emulsion is small, the emulsion is no longer a particulate emulsion but a water-soluble resin, but even the water-soluble resin does not impair the effects of the present invention. The water-based resin in the present invention is a general term for water-dispersed emulsions and water-soluble resins.

Whichever type of base resin is used, the effect of the present invention is not impaired, but epoxy, urethane, and acrylic are more preferable.
In addition, a curing agent such as a blocked polyisocyanate can be arbitrarily added to the water-based resin.

  The metal surface treatment composition of the present invention preferably contains 100 to 1000 ppm of trivalent Bi ions. 150 to 800 ppm is more preferable, and 200 to 600 ppm is most preferable. If the Bi ion concentration is too low, a sufficient amount of Bi adhesion necessary for improving the corrosion resistance cannot be obtained. If the Bi ion concentration is too high, the electrical conductivity of the composition becomes too high, and the coating on the metal material having a complicated shape is increased. As a result, the Bi adhesion amount becomes excessive and the film adhesion may be impaired. The Bi ion concentration in the composition can be determined by solid-liquid separation of the composition using an ultracentrifuge, and the liquid phase can be quantified using high frequency inductively coupled plasma emission spectrometry (ICP) or atomic absorption spectrometry (AA). .

  Bi ion as used herein refers to a Bi component that is not solidified in the composition and is in a completely dissolved state. Specifically, a chelate is constituted by an aminopolycarboxylic acid described later, and is stable. It means that it is in a water-soluble state.

  The composition further contains an aminopolycarboxylic acid. Aminopolycarboxylic acid is a generic term for chelating agents having an amino group and a plurality of carboxyl groups in the molecule. Specifically, EDTA (ethylenediaminetetraacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), NTA (nitrilotrimethyl). Acetic acid), DTPA (diethylenetriaminepentaacetic acid), TTHA (triethylenetetraminehexaacetic acid) and the like are applicable, and EDTA, HEDTA, and NTA are more preferable from the viewpoint of chelate stability with Bi ions.

  The concentration of the aminopolycarboxylic acid is preferably 0.5 to 10 times the molar concentration with respect to Bi ions, more preferably 0.7 to 5.0 times the molar concentration, and 1.0 to 3.0 times the molar concentration. Most preferably. If the concentration ratio with respect to Bi ions is too low, Bi ions are hydrolyzed in the composition and become oxides, so that the effective Bi ion concentration is lowered, and as a result, a sufficient amount of Bi deposition cannot be obtained. On the other hand, if it is too high, Bi ions will be overstabilized and a sufficient amount of Bi will not be obtained.

  In the composition of the present invention, additives usually used in the paint field such as a pigment, a catalyst, an organic solvent, a pigment dispersant, and a surfactant can be further applied as necessary. Examples of pigments include colored pigments such as titanium white and carbon black, extender pigments such as clay, talc and barita, rust preventive pigments such as aluminum tripolyphosphate and zinc phosphate, organic tin compounds such as dibutyltin oxide and dioctyltin oxide, Examples thereof include dialkyltin fatty acids such as dibutyltin laurate and dibutyltin dibenzoate, and tin compounds such as aromatic carboxylates.

  As the liquid medium of the metal surface treatment composition according to the present invention, an aqueous medium is preferable, and water is more preferable. When the liquid medium is water, the liquid medium may contain an aqueous solvent other than water (for example, water-soluble alcohols).

The pH of the composition is not particularly limited, but can be adjusted to a range of usually 2.0 to 7.0, preferably 3.0 to 6.5.
Although there is no restriction | limiting in particular also about the temperature of a composition, When depositing a film | membrane by electrolytic treatment, it can use normally within the range of 15-40 degreeC, Preferably it is 20-35 degreeC.

  Here, the composition according to the present invention contains an aminopolycarboxylic acid, but particularly when combined with a cationic resin, the presence of excess aminopolycarboxylic acid sometimes causes gelation of the cationic resin. There is. In such a case, the amount of the cation group of the cationic resin is reduced or a nonionic resin is used (or the cationic resin and the nonionic resin are mixed, and the total amount of cation groups is relatively reduced. (Decrease) is preferred. By the way, in this case, another problem that the resin does not precipitate so much even when the pH is increased may occur. Here, the problem can be solved by including Al ions. At this time, it is preferable to contain 20 to 500 ppm of Al ions. 50 to 400 ppm is more preferable, and 100 to 300 ppm is most preferable. If the lower limit is not reached, the effect of improving the coating deposition of Al ions becomes insufficient, and if the upper limit is exceeded, the electrical conductivity of the composition becomes excessive, and the throwing power is reduced.

  Here, the mechanism of action of the Al ions described above is as follows. In other words, ionic Al becomes a fine hydroxide colloid due to the increase in pH of the metal surface due to cathode electrolysis, and when it completely loses zeta charge at around pH 9 and begins to agglomerate rapidly, the surrounding resin is also involved and precipitates. Presumed to be.

  A series of reactions from cathodic electrolysis to disappearance of the charge of the hydroxide colloid must be completed instantaneously. If it has become a hydroxide in advance, aggregation starts over time, and the aggregation ability around pH 9 is extremely reduced. Therefore, the Al component in this embodiment must be in the form of ions in the composition.

  In addition, metal ions are usually stabilized by the presence of a chelating agent, but in the case of Al ions, there is no or rare chelating agent that is stable enough to prevent the formation of hydroxide colloid accompanying pH increase. . At least organic acids such as acetic acid, formic acid, sulfamic acid, and lactic acid and aminopolycarboxylic acids that are usually blended in electrodeposition coating compositions do not have a chelating ability to stabilize Al ions.

  Al ions can be added using an Al compound. The Al compound is not particularly limited, but can be added in the form of an inorganic acid salt such as nitrate or sulfate, or an organic acid salt such as lactate or acetate.

Furthermore, in addition to containing Al ions in the above-mentioned range, it is preferable to satisfy the following calculation formula when the pH of the composition according to this embodiment is defined as A [ppm] Al ion concentration.
3.5 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
The following formula is more preferable.
3.6 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
The following formula is most preferable.
3.7 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
When the pH is lower than the lower limit, the deposition efficiency is lowered and the throwing power is also lowered. When the pH exceeds the upper limit, Al ions cause hydrolysis, which is not preferable.

The term -Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 ) is obtained from the solubility product of Al hydroxide at 25 ° C .: 1.92 × 10 ⁻³² . That is, when the pH is exceeded, Al ions precipitate as hydroxides and can no longer be ions. Here, 25 ° C. is a typical temperature during storage and use of the composition.

  Further, the effects of the present invention are not impaired even if the composition of the present invention contains metal ions such as Fe ions, Zn ions, and Ce ions in addition to Bi ions and Al ions. Rather, these metal ions have the effect of promoting the precipitation of the aqueous resin, although not as much as the Al ions. The Fe ion is more preferably trivalent than divalent.

  For reference, the appropriate range of Al ion concentration and pH is shown in FIG.

  In order to form a film on the surface of the metal material after the metal material is immersed in the composition of the present invention, it is necessary to perform cathode electrolysis using the metal material as a cathode. Cathodic electrolysis is an electrolysis process (1) in which electrolysis is performed at a voltage of 0 to 15 V for 10 to 120 seconds and an electrolysis process (2) in which electrolysis is performed at a voltage of 50 to 300 V for 30 to 300 seconds. Need to be performed prior to the electrolysis step (2).

  The electrolysis step (1) is a step mainly performed for preferentially attaching Bi, and the electrolysis step (2) is a step mainly performed for precipitating the resin preferentially. In order to obtain sufficient corrosion resistance, Bi that is in direct contact with the metal material, that is, the presence of the interface Bi existing at the interface between the metal material and the film is required. For this purpose, the electrolysis step (1) and the electrolysis step ( The order and conditions of 2) are extremely important.

  The voltage in the electrolysis step (1) is 0 to 15 V, and electrolysis is preferably performed for 10 to 120 seconds. When the voltage is lower than the lower limit, that is, when electrolysis is performed using the metal material as an anode, the metal material is eluted in the composition, not only reducing the stability of the composition, but also the interface Bi necessary for improving the corrosion resistance. It will not adhere sufficiently. Even when the upper limit is exceeded, resin deposition starts before Bi is preferentially deposited on the metal surface, so that sufficient corrosion resistance cannot be obtained.

  Even when the treatment time is less than the lower limit, sufficient interface Bi is not deposited, and when the treatment time is more than the upper limit, the adhesion amount of the interface Bi becomes excessive, and the adhesion of the film may be impaired.

  The voltage in the electrolysis step (2) is 50 to 300 V, and electrolysis is preferably performed for 30 to 300 seconds. When the voltage is lower than the lower limit, the amount of the resin film deposited is insufficient. When the voltage is higher than the upper limit, the resin film is excessively deposited, which is economically disadvantageous, and the finished appearance of the film may be impaired.

  When shifting to the electrolysis step (2) after the electrolysis step (1), it is not necessary to increase the voltage instantaneously, and even if it is increased slowly, the effect of the present invention is not impaired.

  Bi present in the film obtained by the treatment method of the present invention using the composition of the present invention exists in the form of metal and oxide. Bi deposited by cathodic electrolysis is basically reduced Bi metal Bi, but a part of it is oxidized in particular in the coating baking process to become an oxide. Further, when a high voltage is applied in the electrolysis step (2), the stabilization of Bi by the aminopolycarboxylic acid is insufficient due to the increase in pH of the coating surface, so that it precipitates as oxidized Bi especially on the coating surface side.

  The amount of Bi deposited is preferably 20 to 250 mg / m2, more preferably 30 to 200 mg / m2, and most preferably 50 to 150 mg / m2. If the amount of Bi deposited is too low, sufficient corrosion resistance cannot be obtained. If it is too high, improvement in corrosion resistance can no longer be expected, and film adhesion may be impaired. The amount of Bi attached can be quantified by fluorescent X-ray spectroscopic analysis. The “metal Bi adhesion amount” and “oxidized Bi adhesion amount” in the claims and in the present specification are values determined by the fluorescent X-ray spectroscopic analysis. In addition, the presence of hydroxides cannot be denied as other forms, but when quantified as “metal Bi” or “oxidized Bi” by the measurement method, the numerical value is “metal Bi adhesion amount” or “oxidized Bi”. It is assumed that “the amount of adhesion”.

  The total film thickness of the obtained film is preferably 3 to 40 μm, more preferably 5 to 30 μm, and most preferably 7 to 25 μm. If it is too thin, sufficient corrosion resistance cannot be obtained, and if it is too thick, not only is it economically disadvantageous, but the throwing power may be lowered. The film thickness can be measured by an electromagnetic induction type film thickness meter if the base metal is a magnetic metal, or by an eddy current film thickness meter if the base metal is a non-magnetic metal.

  Bi in the film needs to be present more on the base metal side than the film surface. Specifically, the Bi adhesion amount B on the metal material side from the center of the film thickness is a Bi adhesion distribution in which the total Bi adhesion amount: 55% or more (B / A ≧ 55%) with respect to A. preferable. It is more preferably 58% or more, and most preferably 60% or more. If it is too low, sufficient corrosion resistance cannot be obtained. Note that if it exceeds 90%, the Bi concentration on the surface side of the film is extremely lowered and the function of Bi as a curing catalyst is lost.

  The distribution of Bi adhesion in the film can be measured by line analysis of the film cross section using EPMA. The position of the base metal-coating interface and the coating surface is specified from the backscattered electron images taken at the same time, and the integrated value of Bi intensity in the coating by EPMA line analysis: the integrated value of only the base metal side from the center of A and coating thickness: B can be obtained and B / A can be calculated.

  The contents of the present invention will be specifically described below with reference to examples and comparative examples.

Resin Emulsion Resin Emulsion BASF Cationic Epoxy Resin “Lugalvan EDC” (nonvolatile content: 34%, hereinafter abbreviated “R1”) and DIC Nonionic Urethane Resin “VONDIC2220” (nonvolatile content: 40%, hereinafter abbreviated “ Two types of R2 ") were used.

Pigment Dispersion Paste Japan Epoxy Resin Epoxy Resin “jER828EL” 1010 parts, bisphenol A 390 parts, Daicel Chemical Industries polycaprolactone diol “Placcel 212”, dimethylbenzylamine 0.2 parts, add epoxy equivalent at 130 ° C. The reaction was allowed to reach about 1090.

  Next, 134 parts of dimethylethanolamine and 150 parts of lactic acid (about 90%) were added and reacted at 120 ° C. for 4 hours. Next, methyl isobutyl ketone was added to adjust the solid content to obtain a pigment dispersion resin having a nonvolatile content of 60% by weight.

  15 parts of titanium oxide, 7.0 parts of purified clay, 0.3 parts of carbon black, 1.0 part of dioctyltin oxide, and 3.0 parts of zinc phosphate with respect to 8.3 parts of the pigment dispersion resin obtained above. And 18 parts of deionized water were added and dispersed in a ball mill for 20 hours to obtain a pigment dispersion paste having an inorganic solid content of 50% by weight. This was added so that it might become 5.0 weight% of inorganic solid content in each composition of an Example and a comparative example.

Bi additive Bi compound and aminopolycarboxylic acid were mixed to prepare various Bi additives having a Bi ion concentration of 10,000 ppm.

Bi additive 1 (hereinafter abbreviated as “B1”)
Distilled water: 8.38 g of EDTA was dissolved in 500 g, heated to 60 ° C., bismuth nitrate pentahydrate: 23.21 g was added, and the mixture was stirred until the solid content was completely dissolved. Thereafter, distilled water was further added so that the total amount became 1.0 L, and “B1” was produced. In this case, EDTA has a molar concentration of 0.6 times that of Bi.

Bi additive 2 (hereinafter abbreviated as “B2”)
Distilled water: 13.30 g of HEDTA was dissolved in 500 g and heated to 60 ° C., and then 11.15 g of bismuth oxide was added and stirred until the solid content was completely dissolved. Distilled water was further added so that the total amount finally became 1.0 L, and “B2” was produced. In this case, HEDTA has a molar concentration of 1.0 times that of Bi.

Bi additive 3 (hereinafter abbreviated as “B3”)
After dissolving 39.90 g of HEDTA in 500 g of distilled water and heating to 60 ° C., 11.15 g of bismuth oxide was added and stirred until the solid content was completely dissolved. Distilled water was further added so that the total amount finally became 1.0 L, and “B3” was produced. In this case, HEDTA has a molar concentration of 3.0 times that of Bi.

Bi additive 4 (hereinafter abbreviated as “B4”)
Distilled water: NTA: 73.12 g was dissolved in 500 g and heated to 60 ° C., and then bismuth oxide: 11.15 g was added and stirred until the solid content was completely dissolved. Distilled water was further added so that the total amount was finally 1.0 L, and “B4” was produced. In this case, NTA is 8.0 times the molar concentration of Bi.

Preparation of Composition A composition was prepared by blending a pigment dispersion paste having an inorganic solid content of 5.0% by weight with a resin emulsion and Bi additive in the combinations shown in Table 1. Each concentration was adjusted by diluting with deionized water. Further, the pH of the composition was adjusted with nitric acid or ammonia as necessary.

SUS304 was used for the anode electrode as the electrode opposite to the electrolysis conditions , the anode / cathode pole ratio was 1.0, and a predetermined potential was applied by a rectifier. When performing the cathode electrolysis treatment, the temperature of the composition was kept at 30 ° C. by a heat exchanger and stirred by an impeller. Each detailed electrolysis condition is shown below. Each electrolytic pattern is shown in FIG.

Electrolysis condition 1 (hereinafter abbreviated “E1”)
After the electrolysis at 13V for 15 seconds as the electrolysis step (1), the electrolysis process was immediately performed at 280V for 45 seconds as the electrolysis step (2).
Electrolysis condition 2 (hereinafter abbreviated as “E2”)
After electrolysis at 8V for 60 seconds as the electrolysis step (1), an electrolysis treatment was immediately performed at 180V for 180 seconds as the electrolysis step (2).
Electrolytic condition 3 (hereinafter abbreviated as “E3”)
As an electrolysis step (1), electrolysis was performed at 2 V for 110 seconds, and immediately thereafter, electrolysis was performed at 60 V for 290 seconds as an electrolysis step (2).
Electrolysis condition 4 (hereinafter abbreviated as “E4”)
In the electrolysis step (1), the pressure was increased from 0 V to 15 V over 60 seconds, and further increased to 50 V over 30 seconds. Then, in the electrolysis step (2), the pressure was increased to 200 V over 30 seconds, and 200 V was maintained for 120 seconds. . As a result, the electrolysis step (1) in claim 4 takes 60 seconds, and the electrolysis step (2) takes 150 seconds.
Electrolysis condition 5 (hereinafter abbreviated as “E5”)
As an electrolysis process (1), an electrolysis process was performed at 210 V for 160 seconds, and an electrolysis process (2) was not performed.

As a test plate , a cold rolled steel plate: SPCC (JIS 3141) 70 × 150 × 0.8 mm (hereinafter abbreviated as SPC) is used, and its surface is preliminarily strong alkaline degreasing agent “FC-E2001” manufactured by Nihon Parkerizing Co., Ltd. Was degreased by spraying for 120 seconds. After degreasing treatment, it was washed with spray water for 30 seconds, immersed in the compositions shown in Examples and Comparative Examples, and subjected to cathode electrolytic treatment under the electrolytic conditions shown in Examples and Comparative Examples. The test plate after completion of electrolysis was immediately rinsed with deionized water for 30 seconds and baked at 180 ° C. for 20 minutes in an electric oven.

Investigation of film characteristics The film characteristics of the film deposited on the test plate were investigated by the following method.
Film thickness measurement: Measured using an electromagnetic induction film thickness meter.
Bi adhesion amount: quantified by fluorescent X-ray spectroscopic analysis.
Bi adhesion distribution: Sample cross section was analyzed by EPMA line analysis. See below for specific methods.

  Bi adhesion amount distribution measurement in the film was analyzed using EPMA. The metal material after the film treatment was fixed with an embedded resin, the cross section was polished, and a line analysis profile of Bi was obtained from the base metal direction to the deposited film surface direction. A line analysis profile is an average value of characteristic X-ray intensity calculated in an arbitrary width in the one-dimensional direction of an analysis area based on mapping analysis data, and can be interpreted as a line analysis having a width. The measurement conditions are as follows.

Measuring instrument: EPMA-1610 electron gun manufactured by Shimadzu Corporation: CeB6 cathode beam current: 50 nA, beam voltage: 15 kV, beam diameter: 1 μmφ or less Integration number: once, sampling time per point: 100 ms
Spectroscopic crystal: PET (Bi Mα)

The position of the interface between the base metal and the film and the surface of the film is specified from the backscattered electron image taken at the same time, and the integrated value of Bi intensity in the film: A and the integrated value only on the base metal side from the center of the film thickness: B are obtained. B / A was calculated.
For reference, FIG. 2 shows the analysis result of the film obtained in Example 4 as a representative profile.

Corrosion Resistance Test Method and Evaluation Method A crosscut was applied to the electrodeposited coated plate, a salt spray test (JIS-Z2371) was performed, and the maximum swell width on one side of the crosscut portion after 1000 hours was measured. Based on the measurement results, the evaluation was made with less than 2 mm: ◎, 2 mm or more and less than 3 mm: ○, 3 mm or more and less than 4 mm: Δ, 4 mm or more: x.
The results are shown in Table 1.

  From Examples 1 to 6 in Table 1, by applying the treatment method of the present invention using the composition of the present invention, the film of the present invention capable of ensuring sufficient corrosion resistance to the metal material is obtained. I understand that.

  On the other hand, Comparative Example 1 was at the same level as Example 1 except that Bi ions and Zn ions were added excessively, but the total metal ion concentration in the composition was excessive, and the amount of Bi attached was excessive. In addition, a sufficient film thickness could not be obtained, and the corrosion resistance was insufficient.

  Comparative Example 2 is a level in which the Bi ion concentration of Example 4 was reduced and the electrolysis conditions were changed, but not only a sufficient amount of Bi was obtained, but also Bi coating on the base metal surface was insufficient (B / A deficiency). Thus, sufficient corrosion resistance could not be obtained.

Further, in Comparative Example 3 in which neither Bi nor aminopolycarboxylic acid was added, the effect of Bi was not obtained at all, and the corrosion resistance was insufficient.
Further, in Comparative Example 4 in which the resin concentration in Example 6 was reduced and the additive metal was not added, the effect of the additive metal as a film deposition improver was not obtained in addition to insufficient resin concentration. There wasn't.

As described above, a coating capable of imparting sufficient corrosion resistance to a metal material by cathodic electrolysis under appropriate electrolysis conditions using a resin emulsion aqueous solution containing Bi ions and aminopolycarboxylic acid, which is a feature of the present invention. That is, it was confirmed that the resin film having a sufficient and effective Bi adhesion amount and Bi adhesion distribution can be deposited.

Claims (4)

5 to 30% by weight of nonionic and / or cationic aqueous resin, 100 to 1000 ppm of trivalent Bi ion, and 0.5 to 10 times molar concentration of aminopolycarboxylic acid with respect to Bi ion A composition for electrodeposition coating . The composition for electrodeposition coating according to claim 1, comprising 20 to 500 ppm of trivalent Al ions.   After the surface-cleaned metal material is immersed in the composition according to claim 1 or 2, the electrolysis step (1) using the metal material as a cathode, that is, a voltage of 0 to 15 V for 10 to 120 seconds. Including an electrolysis step and an electrolysis step (2), that is, a step of electrolysis for 30 to 300 seconds at a voltage of 50 to 300 V, and the electrolysis step (1) is electrolyzed prior to the electrolysis step (2), followed by washing with water and A metal surface treatment method characterized by depositing a film on a metal material by baking.   Using the composition according to claim 1 or 2, the treatment method according to claim 3, metal Bi and oxidized Bi are deposited as Bi in an amount of 20 to 250 mg / m 2, the total film thickness is 5 to 40 μm, and Metal surface, characterized in that the Bi adhesion amount on the metal material side from the center of the coating thickness: B is a Bi adhesion distribution that is 55% or more (B / A ≧ 55%) with respect to the total Bi adhesion amount: A Treatment film.

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